Internal combustion engines of the present invention exhibit improved fuel economy, lower pollution and superior operating characteristics relative to engines in use or currently proposed as of the date of this document. Currently in common use are four cycle-spark ignition (SI) and four-cycle compression ignition (CI) engines. In both cases, four phases of the cycle correspond to strokes of the piston: intake, compression, expansion, and exhaust.
FIG. 2 is an ideal gas diagram which is useful when considering theory of operation of four-cycle engines and engines of the present invention. FIG. 2 plots pressure as a function of volume for a charge of gas in an engine during the four phases. The area inside the enclosed curves is proportional to the work done per cycle by the gas. During the intake and compression phases, the gas is drawn into a chamber, and then compressed, respectively. The compression phase is shown by a movement from point A to B in FIG. 2. Point A is the point of maximum cylinder volume, and point B is the point of minimum cylinder volume. The path traced by the line A-B is considered to be adiabatic, that is, without loss or gain of heat. In the CI engine, only air is compressed. In the SI case, the air is premixed in a precisely controlled fashion with fuel vapor at point A using a ratio of about 14.3 to 1 by weight, and then compressed. In the SI case, the combustion process is started by a spark which occurs near point B in the cycle. In the CI case, the combustion process is started when the fuel is either directly injected into the cylinder, or indirectly injected into a prechamber connected to the main cylinder. The superheated air initiates the combustion. In both cases, as the fuel burns, the pressure rises and work is done to push the piston downward. This is the expansion cycle, and it is represented on FIG. 2 as B-G-D-E. At the point E, the end of the expansion cycle, the exhaust valve opens and the remaining compressed exhaust gases are released with a resultant loss of energy during the exhaust stroke or phase. This process is sometimes termed "exhaust blow down." This lost energy is represented by the area E-F-A. Point A represents the termination of expulsion of exhaust gases from the engine, and the cycle is repeated.
Three models are used for the addition of heat to the compressed gas in internal combustion engines. The first is the Otto cycle, which is shown by A-B-C-D-E, and also known as a constant volume cycle. The second is the Diesel cycle, which is shown by A-B-D-E, and also known as a constant pressure cycle. The third is a limited-pressure cycle, which is not shown, and contains some constant volume expansion, followed by some constant pressure expansion. Another model, which is used in gas turbines, is the Brayton (Joule) cycle. This model consists of adiabatic compression, followed by constant pressure heat addition, followed by adiabatic expansion down to atmospheric pressure. This model best describes the present invention's operation.
Practical engines, both SI and CI, usually fail to reach maximum theoretical pressure represented by point C in the pressure-volume diagram of FIG. 2; instead, the maximum pressure is usually encountered at a point such as G on that diagram. CI engines typically reach higher pressures than SI engines, however. The area enclosed by these curves is the amount of energy available to do mechanical work. Highest temperatures and pressures will be encountered in the area B-G-D of the diagram, and it is at the high temperatures and pressures that nitrous oxides are formed.
It is an object of the present invention to provide an engine that will more closely follow the Brayton cycle, limiting the production of nitrous oxides. It is also an object of the present invention to utilize the energy in the area A-E-F as shown in FIG. 2 by employing full expansion of the exhaust gases. Other desirable operating characteristics will also be realized.
Three goals in engine design are efficiency (maximum work output for fuel consumed), high power output for engine size and weight (or specific output), and low pollution, especially hydrocarbons and nitrous oxides. Following is a summary of the characteristics of SI and CI engines.